Comparison of force-time parameters and EMG in static explosive gripping by various exertion conditions: muscle...

The purpose of this study was to compare the exertion and electromyography (EMG) properties during the developmental phase (DFmax) in static explosive grip (SEG), rapid submaximal exertion grip, namely fake SEG exertion (FAKE), and SEG in a muscle fatigue state.

Thirty healthy males and females performed the SEG and FAKE exertions (50% and 75% of peak value as a target value). Then, they performed sustained repeated rhythmic grip for 6 min (30 times x min(-1)), and SEG after 1-min, 4-min, and 7-min (SEG after the exertion). EMG was measured concurrently to compare with the muscle activation property during each grip exertion. Eight force-time parameters evaluating the DFmax in addition to the peak value were selected.

The peak value significantly decreased, and the mean power spectrum density shifted to the low-wave in SEG after the exertion as compared with before. Therefore, SEG after the exertion was judged to be a muscle fatigue state. In addition, because the frequency properties in each exertion differed, the muscle activation properties during their DFmaxs were considered to differ. From the comparison between SEG before and after the exertion and FAKE, it is suggested that the time of reaching the peak value and the relative muscle strength when reaching an inflection point are not useful as parameters to evaluate the explosive muscle function during SEG.

The maximal increasing volume during the DFmax and integrated area until 0.25 and 0.5 s could discriminate a difference of the DFmaxs according to each exertion and they are useful parameters.